how to reduce clump of strange noise in render?
It looks like noise from reflective or refractive caustics or something simlar. Try disabling &quot;Reflective Caustics&quot; and / or &quot;Refractive Caustics&quot; in the Caustics section under &quot;Light Paths&quot;. If the noise disappears, try re-enabling caustics and in the &quot;Clamping&quot; section set a value for &quot;Indirect Light&quot;, like 10 or 5.